Hmm...what else? What are the primary Extraordinary Abilities that pose hazards to someone using Antimagic Field a lot?

I'd say keep an eye out for Hulking Hurlers and other uber-big hazards. I remember getting almost killed by these brute snipers with one boulder chuck, which inspired my Cheater to grab resistance to non-magical damage. Even then, some crazy monsters can throw things so big they don't count as damage anymore - they become crushing hazards, against which damage resistances/immunities don't work. No Antimagic Field is going to work against a mountain falling down on top of you.

This is a thing. Aside from Initiate of Mystra and doughnut-AMFs (which always felt wrong to me, since it's an emanation - how does that even work?), which are honestly super-cheesy (though the ring AMF is nowhere near as good since it doesn't actually protect you vs enemy spells, and you really have to position yourself right).

It's probably best to cast AMF via an item. If you can get custom items, some magic armour of AMF or something is a pretty good shout, and at very high levels you may as well splash for a Widened AMF because aside from tomes and grafts, what else are you going to spend your money on?

The Antimagic Grappler is the classic strategy. Grappling is already pretty nasty when people don't have Freedom of Movement up; AMF makes that pretty much a cert. Otherwise you likely want to AoO tank and use stuff like Stand Still. If people can just walk out of your AMF, it's not that effective.

I've actually made (several incarnations of) a character who uses this as his shtick. I mostly took funky templates and PrCs which boosted Strength (Green Star Adept for the win!) and relied on Antimagic Torcs. However I've never gotten to play him - and honestly I'm not sure if it would even be that fun. AMF is just a bit too all-or-nothing; having to deal with it very occasionally can be an interesting challenge but I think a game would become kind of boring if it showed up every fight. It's a great theoretical optimisation thing, but not so much in practice.

Mm...on a bit of a tangent, does anyone know any rules for inventing/crafting the futuristic weapons described in the DMG? Page 146? The laser pistols and antimatter rifles? If you needed a weapon to use in an antimagic field...

Agree with TheFred. It's a fun optimization concept but in an actual game it will result in the DM being extremely limited in what can be thrown at you. This not only will make the game less fun overall, but will encourage the DM to tailor encounters specifically to counter your AMF build. Also, it's just munchkin-y as all hell.

But, if you really want to go down that route, find a way to be a dragon that can cast AMF.

The Antimagic Grappler is the classic strategy. Grappling is already pretty nasty when people don't have Freedom of Movement up; AMF makes that pretty much a cert.

I had an AMF grappler in an arena that did pretty well. Dragonborn (Wings) Goliath Cleric / Warblade with some grafts (the blindsense one to find invisible enemies). Cleric was so he could use a staff of AMF with ease, and Warblade was for Crushing Weight of the Mountain stance so he could constrict people while grappling.

In a one-on-one fight it is a great strategy. But in a "real" game where there is a battlefield full of people that can attack you while you're grappling, it does make you somewhat vulnerable.

There is also Otiluke's Suppressing Field spell from Complete Mage. It basically works like an AMF but against just 1 specific school of magic at a time. So if you know you are about to fight a necromancer, just use the OSF attuned to necromancy and save yourself the hassle of shutting down your own items and spells.